Hydraulic lift return control means



Feb. 18, 1958 L. s. WOOD HYDRAULIC LIFT RETURN CONTROL MEANS 2 Sheets-Sheet 1 Filed Jan. 28. 1957 INVENTOR. 400/5 5. W000 4 rroe/ve'y Feb. 18, 1958 s. WOOD 2,823,648

HYDRAULIC LIFT RETURN CONTROL MEANS Filed Jan. 28, 1957 2 Sheets-Sheet 2 INVENTOR. 100/5 5. W000 United States Patent HYDRAULIC LIFT RETURN CONTROL MEANS Louis S. Wood, Findlay, Ohio Application January 28, 1957, Serial No. 636,651

6 Claims. (Cl. 121-46) This invention relates to means for controlling the rate of gravity return of hydraulically lifted items such as power operated tail gate mechanisms disclosed and claimed in Patent No. 2,469,321 issued to Louis S. Wood on May 3, 1949. It should be understood that the present invention is equally applicable to other hydraulically operated devices such as dump truck bodies and the like which are lifted or tilted hydraulically and return totheir normal position by gravity.

In all such devices, particularly extremely heavy items or devices of the type that are raised or lifted hydraulically by a hydraulic power cylinder, the gravity return thereof when the hydraulic pressure in the power cylinder is released becomes extremely rapid. The use of hand control valves which may be partially opened or cracked to control the lowering or return of the item or load lifted by the power cylinder is hazardous inasmuch as failure to properly partially open or crack' the valve controlling the release of hydraulic pressure from the power cylinder would cause the item or load to drop too rapidly. Under such conditions, damage would be done to the structure or load being lowered, or, the structure or load might accidentally be dropped on the foot or hand of a workman who would not have ample opportunity to escape from the hazard.

With the foregoing in view, the primary object of the inventionis to provide an improved, simple and inexpensive yet positive method and means for controlling the gravity return of hydraulically lifted items such as tail gates, dump bodies, and other items lifted by a hydraulic power cylinder when pressure is applied thereto which return by gravity when the lifting pressure is released from the power cylinder.

A further object of the invention is to provide a completely automatic means for controlling the rate of gravity return of items elevated by a hydraulic power cylinder and returned by gravity responsive to the release of hydraulic pressure on said power cylinder.

Other objects of the invention will become obvious by reference to the following detailed description taken in connection with the accompanying drawings in which:

Fig. 1 is a longitudinal sectional" view through a hyv draulic lift return control means embodying the invention in its neutral position.

Fig. 2 is a diagrammatic view showing a hydraulic circuit of a hydraulic power cylinder of the type used to raise the hydraulic tail gate shown in Fig; 7, the main control valve being in its neutral or load holding position with no hydraulic pressure applied to the power cylinder or released therefrom.

Fig. 3 is a longitudinal sectional view similar to Fig. 1

showing the hydraulic lift return control means in its ,7 2,823,648 Patented Feb. 18, 1958 hydraulic pressure from the power cylinder to lower the load.

Fig. 5 is a longitudinal sectional view similar to Figs. 1 and 3 showing the hydraulic lift return control means in its load raising position.

Fig. 6 is a diagrammatic view of the said hydraulic circuit similar to Figs. 2 and 4 except that the main control valve has been moved to its load raising position applying hydraulic pressure to the power cylinder to lift the load.

Figs. 7 and 8 are side elevational views of a hydraulically operated tail gate mechanism in its raised and lowered position respectively, the power cylinder of which may be operated by the illustrative embodiment of the invention and illustrative hydraulic circuit herein described.

Referring now to the drawing wherein like numerals refer to like and corresponding parts throughout the several views, the hydraulic lift return control means 10 embodying the invention will now be described in connection with a hydraulically operated tail gate mechanism and preferred hydraulic circuit employed to operate the same, it being understoood that the particular application of the said hydraulic lift return control means 16 is intended to be illustrative only inasmuch as the invention may be applied to many other hydraulically powered and gravity return devices.

In Figs. 2, 4 and 6, the hydraulic circuit illustrated preferably employed to operate the power cylinder 59 of a power lift and gravity lowered mechanism such as the tail gate construction shown in Figs. 7 and 8 comprises a pump 51 having its inlet connected to an oil reservoir 52 and itsdischarge connected to a three-way operating valve 53. The said operating valve 53 has outlets connected to a pressure relief valve 54 and the hydraulic lift return control means 10. The relief valve 54 is connected to the oil reservoir 52 while the hydraulic lift return control means 10 is connected to one end of the power cylinder 50 so that fluid entering the said cylinder 50 from the said hydraulic lift return control means urges the piston 55 on its power stroke. The opposite end of the cylinder 50 is connected to the said reservoir 52. The said cylinder 50 is connected by a pivot pin 81 to a fixed element such as a truck body 800, and the piston rod 55d of the piston 55 is connected by a pivot pin 82- to a lever 83 and through suitablelinkage 84 to the platform 85 of the tail gate construction 80 or the like to be raised on the power stroke of the said piston 55. The said platform 85 of the tail gate construction 89 or the like is lowered responsive to gravitation during the return stroke of the said piston 55 under control of the said hydraulic lift return control means 10.

When the three-way operating valve 53 is in its neutral or N position shown in Fig. 2, the tail gate platform 85 is hydraulically locked in any elevated position it has assumed at the moment the said operating valve 53 is moved to its said neutral or N position.

Assuming the tail gate platform 85 is in an elevated position such as shown in Fig. 7, and the three-way operating, valve 53 is moved from its neutral position N shown in- Fig. 2 to its lowering or L position shown in Fig. 4, the said tail gate platform 85 lowers by gravity under the control of the said hydraulic lift control means 10,. the piston 55 moving downwardly as viewed in Fig. 4 urging fluid back to the reservoir 52 through the said hydraulic lift return control means 10.

Assuming the tail gate platform 85 is in a lowered position as shown in Fig. 8, and the three-way operating valve 53 is moved from its neutral position N shown in Fig. 2 to its raising position R shown in Fig. 6, the said tail gate platform 85 raises under hydraulic pressure by fluid" applied to' the piston 55 moving freely from the pump 51 through the three-way operating valve 53 and the hydraulic lift control means to to the power cylinder 50, the said piston 55 moving upwardly as viewed in Fig. 6. I

The illustrative embodiment of the hydraulic lift return control means 10 shown in its different operating positions in Figs. 1, 3 and 5 consists of a housing 11 having a valve spool bore 12 therethrough into which a valve spool 13 is 'reciprocatingly mounted. The said valve spool 13 comprises an integrally formed pistcn 14. stem 15 and guide 16, the said guide 16 being spaced longitudinally from the piston 14. The said housing- 11 is cored out to provide an interior wall 110 forming interior valve chambers A and B when the valve spool 13 is positioned in the valve spool bore 12. The said valve spool bore 12 provides a communicating passage 12a between the said valve chambers A and B when the valve spool 13 of the hydraulic lift return control means is in its neutral position as shown in Fig. l. The housing 11 is provided with threaded ports 17 and 18 communicating with the valve chambers A and B respectively through which hydraulic fluid passes into and out of the said hydraulic lift return control means 10.

A combined end cap and stop 20 is secured by suitable studs 21 onto the end of the housing 11 over the open end of the valve spool bore 12, the said end cap 2!) covering the extreme end of the piston 14. A gasket 22 is employed to make the joint between the housing 11 and the end cap 20 fluid tight. The said end cap 2% is so formed as to provide a pressure chamber 2% into which the end of the piston 14 of the valve spool 13 travels when the said hydraulic lift return control means is in its neutral position as shown in Fig. 1. The opposite end of the housing 11 is closed by an end cap 23 secured to the said housing 11 by means of bolts 24. A gasket 25 is provided to seal the joint between the housing 11 and the end cap 23. The said end cap 23 is centrally bored at 230 to guide the stem 15 of the valve spool 13 which reciprocates therethrough. An O-ring 26 provides a suitable fluid tight seal between the said valve spo l stem 15 and the centrally bored end cap 23.

A stop sleeve 27 is positioned within the valve spool bore 12 and against the inner face of the end cap 23, which stop sleeve 27 is contacted by the guide 16 of the valve spool 13 to limit the movement of the said valve spool 13 to the left as viewed in Figs. 1, 3 and 5. Weep holes 160 are provided in the guide 16 to prevent entrapment of hydraulic fluid in that portion of the valve spool bore 12 between the guide 16 and the end cap 23.

A suitable compression spring 28 is provided around the stem 15 of the valve spool 13 between the guide 16 thereof and the end cap 23 to constantly urge the said valve spool toward its neutral position as viewed in Fig. l with the extreme end 140 of the piston 14 thereof disposed against the combined stop and end cap 20. The said extreme end 140 of the piston 14 is preferably formed in a conical shape to permit hydraulic fluid to flow therebehind to move the said valve spool to the left against the pressure of the compression spring 28 from the position shown in Fig. 1 to the position shown in Figs. 2 and 3. The stem 15 of the valve spool 13 between the piston 14 and the guide 16 thereof is formed sufliciently large to provide a hydraulically unbalanced condition of the said valve spool 13 when fluid under pressure exists at both ends of the piston 14 thereof.

The interior wall 111 of the said housing 11 is provided with a combined passage and ball valve seat 30 opposite which the housing 11 is provided with a threaded aperture 31 plugged with a plug 32. The inner end of the plug 32 is bored at 33 to accommodate a spring 34 which constantly urges the ball valve 35 on its seat 30. The said ball valve 35 provides communication between valve chambers A and B to permit passage of hydraulic fluid through the said hydraulic lift return control means when the valve spool '13 thereof is in its load raising position shown in Fig. 5.

The said interior wall 111 of the said housing 11 is also provided with relatively small bores or passages 36 and 37. The passage 36 communicates between valve chambers A and B, while the passage 37 communicates between the valve chamber A and the pressure chamber 239 in the combined end cap and stop 20.

In its operation, the hydraulic lift return control means 10 is fully automatic and functions responsive to the direction of flow and pressure of hydraulic fluid therethrough when connected in a suitable hydraulic circuit to a power cylinder, the said hydraulic circuit and power cylinder being arranged to lift items responsive to the application of hydraulic fluid under pressure to the power cylinder and to lower such items responsive to release of hydraulic fluid under pressure from the said power cylinder created by the weight of the load thereon.

In the illustrative embodiment of the invention, assuming that the tail gate platform has been lifted to its fully elevated position and the operating valve 53 is moved to its neutral or N position as shown in Figs. 1 and 2, no fluid can pass through the hydraulic circuit or the hydraulic lift return control means 10 except from the hydraulic fluid reservoir 52 to the pump 51, through the three-way operating valve 53, through the pressure relief valve 54, and back to the said hydraulic fluid reservoir 52. Therefore, the valve spool 13 of the said hydraulic lift return control means 10 remains static in its neutral or N position shown in Fig. 2 under the pressure of the compression spring 28.

When the operating valve 53 is moved from its neutral or N position shown in Fig. 2 to its lowering or L position shown in Fig. 4, hydraulic fluid under pressure flows immediately from the power cylinder 50 to the valve chamber A of the hydraulic lift return control means 10 from whence it flows to the valve chamber B through the communicating passage and the bore 36. Simultaneously hydraulic fluid under pressure from the valve chamber A enters the pressure chamber 200 through the bore 37, acts on the conical end of the piston 14, overcomes the spring pressure of the compression spring 28 on the valve spool 13, and moves the said valve spool 13 to the left from its neutral or N position shown in Fig. l to its lowering or L position shown in Fig. 3. After the said valve spool 13 is so moved, the only flow of hydraulic fluid from the power cylinder 50 through the hydraulic lift return control means 10 passes through the bore 36, and, since the bore 36 is sized to restrict the flow of hydraulic fluid through the said hydraulic lift return control means, the said restricted flow governs the rate of gravity return of the tail gate platform 85. The strength of the compression spring 28 is preferably selected to permit a relatively rapid lowering of the tail gate platform 85 when unloaded by preventing movement of valve spool 13 from its neutral or N position shown in Fig. 1 to its lowering or L position shown in Fig. 3. In which case, the rate of lowering of the unloaded tail gate platform 85 is governed by the normal resistance to the flow of hydraulic fluid from the power cylinder 50 to the reservoir 52.

Assuming that the tail gate platform 85 is in its lowered position and the operating valve 53 has been moved to its neutral or N position, the said tail gate platform 85 is raised by moving the operating valve 53 to its raising or R position as shown in Fig. 6 whereupon hydraulic fluid under pressure passes from the reservoir 52 to the pump 51, through the three-way operating valve 53, through the hydraulic lift return control means 10 and to the power cylinder 50 as shown in Figs. 5 and 6. Immediately upon moving the operating valve 53 from its neutral or N position to its raising or R position, hydraulic fluid flows from chamber B of the hydraulic lift return control means 10 through the communicating passage 120 and the bore 36 into and through chamber A thereof to the power cylinder 50. Hydraulic fluid under pressure in chamber A immediately passes therefrom into the pressure chamber 209 through the bore 47 whereupon pressure therein acts on the conical end 140 of the piston14 to movethe spool valve 13 from its neutral position shown in Fig. l to its raising position shown in Fig. 5. Since the bore or passage 36 from chamber B to chamber A is not sufliciently large to accommodate the desired'flow of hydraulic fluid from the chamber B to the chamber Awhen the said spool valve 13 is in its raising position shown in Fig. 5, the pressure in chamber B opens the ball valve 3'5'and an adequate flow of hydraulic fluid passes through the hydraulic lift return control means to permit the power cylinder 50 to raise the tail gate 85 whether loaded or unloaded.

It is preferable that the three-way operating valve 53 be of a type that the neutral'N position thereof is located between its lowering L and its raising R positions as indicated in Figs. 2, 4 and6.

Although but a single embodiment of the invention has been disclosed and described in detail, and but one application of the invention has'been'illustrated, itis obvious that many changes may be made in the size, shape, arrangement and detail of the various elements of the invention and in its application to hydraulically lifted and gravity return devices, all without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A hydraulic lift return control means comprising a housing having a main passage therethrough adapted to be connected into the hydraulic power pressure and return pressure line to and from a power cylinder, the said housing having a valve spool bore therein, a valve spool reciprocatingly mounted in said bore including a piston at one end thereof adapted to close said main passage through said housing when the said valve spool is moved to its operating position, the said housing having a pressure chamber formed therein at the piston end of said valve spool bore with a fluid passage thereto admitting hydraulic fluid under pressure therein to move said valve spool to its op erating position and close said main passage through said housing, spring means urging said piston to its neutral position whenever insuflicient pressure exists in said pressure chamber to move said valve spool to its operating position, the said housing having also a restricted passage therethrough permitting either a restricted power pressure flow or a restricted return pressure flow of hydraulic fluid in opposite directions through the hydraulic lift return control means, and valve means openable only responsive to a power pressure flow of hydraulic fluid through said hydraulic lift return control means whereby to permit a relatively free power pressure flow of hydraulic fluid therethrough.

2. A hydraulic lift return control means for controlling the rate of return of a load lifted or supported by a hydraulic power cylinder comprising a housing having a partition therein with a main passage therethrough adapted to be connected into the hydraulic power pressure and return pressure line to and from said power cylinder, the said housing having a valve spool bore there in, a valve spool reciprocatingly mounted in said bore including a piston at one end thereof adapted to close said main passage when the said valve spool is moved to its operating position, the said housing having a pressure chamber formed therein at the piston end of said valve spool bore with a fluid passage thereto from said main passage through said housing admitting hydraulic fluid under pressure to said pressure chamber causing said piston to move said valve spool to its operating position and close said main passage through said housing, spring means urging said piston to its neutral position whenever insuflicient pressure exists in said pressure chamber to move said valve spool to its operating position, the said housing having also a restricted passage therethrough permitting a restricted power pressure and a restricted return pressure flow of hydraulic fluid in opposite directions through the hydraulic lift return control means, and valve 6 means openable only responsive to a power pressure'flow of hydraulic fluid through said hydraulic lift return control means whereby to permit a relatively free power pressure flow of hydraulic fluid therethrough.

3. A hydraulic lift return control means for controlling the rate of return'of a load: lifted by a hydraulic power cylinder having a power pressure and power return line thereto comprising a housing partitioned to provide a pair of chambers therein and ported for connecting the same into the said hydraulic power pressure and return pressure line, the said housing having a valve spool bore therein providing a passage between said" chambers, a valve spool reciprocatingly mounted in said bore including a piston at one end thereof adapted to close said passagebetween said-chambers when the said valve spool is moved to its operating position, the said' housing in-' cluding means forming a pressure chamber at the piston end ofsaid valve spool bore serving as a'n'eutral stop for said piston, spring means urging said piston and valve spool to its neutral position, the strength of said spring determining the pressure required in said pressure chamber to move said valve spool to its operating position, the said housing having a passage therein to said pressure chamber admitting fluid under pressure thereto from one of said first mentioned chambers to move the said valve spool to its operating position and close said passage between said chambers, a normally closed valve means in the partition between said first mentioned chambers openable only responsive to a power pressure flow of hydraulic fluid pressure through said hydraulic lift return control means whereby to permit a relatively free power pressure flow of hydraulic fluid therethrough during the power stroke of said power cylinder, and a constantly open restricted passage in said partition between said first mentioned chambers permitting only a restricted return pressure flow of hydraulic fluid through the hydraulic lift return control means during the return stroke of said power cylinder.

4. Means for controlling the rate of gravity return of a load lifted by the piston of a hydraulic power cylinder to which hydraulic fluid under power pressure is supplied in one direction through a hydraulic pressure and return line to lift said load and from which hydraulic fluid is returned in said line in the opposite direction under a return pressure created by said load on said piston, said return control means being connected in said pressure and return line and comprises a housing having a fluid passage therethrough, a valve spool including a piston reciprocatingly mounted in said housing spring urged to a neutral position to maintain said passage open, a pressure chamber in said housing at the piston end of said valve spool, the said housing having a passage therein to said pressure chamber admitting hydraulic fluid therein to move said valve spool to its operating position and close said passage responsive to the flow of fluid under pressure through said valve in either direction, the said housing also having a constantly open but restricted passage therethrough governing the return pressure flow of hydraulic fluid through said return control means during the return stroke of said power cylinder, and a second spring loaded valve means within said housing operable responsive only to the power pressure flow of hydraulic fluid through said return control means permitting a relatively free flow of hydraulic fluid therethrough during the power stroke of said power cylinder.

5. In a hydraulic lift return control means for use in the hydraulic fluid pressure and return line of a hydraulic power cylinder arranged to lift a load during a pressure flow of hydraulic fluid thereto and permit a controlled rate of gravity return of the load responsive to a restricted return flow of hydraulic fluid therefrom, a housing including an interior wall therein forming a return flow and pressure flow valve chamber and having a valve spool bore therethrough providing a passage between said valvechambers, the said housing having ports therein for connecting said valve chambers in said pressure and return line with the return flow port positioned toward said power cylinder, a valve spool including a piston at one end thereof reciprocatingly mounted in said valve spool bore, the said housing including means forming a pressure chamber at the piston end of said valve spool bore serving as a neutral position stop for said valve spool, spring means urging said valve spool to its neutral position against said stop, the said housing having a passage therein connecting the return flow chamber to said pressure chamber, the said valve spool piston closing the spool bore passage between said valve chambers when said valve spool is moved hydraulically from its neutral position to its operating position responsive to hydraulic fluid under pressure entering said pressure chamber during either the return flow or pressure flow of hydraulic fluid through the hydraulic lift return control means, the said interior wall of said housing having a restricted passage therethrough limiting the rate of flow of hydraulic fluid from the return flow chamber to the pressure fluid chamber when said valve spool is moved to its operating position during the return flow of hydraulic fluid from said power cylinder, and a normally closed valve means in said interior wall openable only responsive to the pressure flow of hydraulic fluid from the pressure fluid chamber to the return flow chamber when said valve spool is moved to its operating position during the pressure flow of hydraulic fluid through the hydraulic lift return control means to said power cylinder.

6. A hydraulic lift return control means as claimed in claim 5 wherein the said compression spring is of suflicient strength to prevent the said valve spool from moving to its operating position unless a predetermined pressure is developed in said pressure chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,495,785 Stephens Jan. 31, 1950 2,501,483 Taylor Mar. 21, 1950 2,753,849 Becker July 10, 1956 

